1. Field of the Invention
This invention relates to an end face seal for sealing the space between a rotating shaft and its housing. This seal has particular benefits when used in gas turbines or compressors which have a shaft diameter in excess of three inches and which generate high pressures.
2. Description of the Prior Art
Prior to my invention, radial oil seals have been utilized in these environments. Basically these seals take the form of two or more radial sealing rings which closely surround the rotating shaft and are affixed to the housing in a sealing arrangement. Oil at a pressure in excess of the gas pressure is then pumped from a reservoir to an annular chamber defined by a gap between the sealing rings. From the annular chamber, oil then flows between rotating shaft and the sealing rings, preventing gas leakage and thereby effecting the gas sealing function. These radial oil seals, while sufficient to protect against fluid loss, have numerous design disadvantages. These include an expensive oil cooling and oil circulating systems, an oil reservoir, complexity and cost. In addition such seals have functional disadvantages including potential contamination of the gas with the associated housing and pipeline, and a large consumption of energy.
Others have recognized some of these disadvantages and sought to provide a substitute for the rotary oil seal for gas compressors. On such seal is a rotary seal depicted in U.S. Pat. No. 3,575,424 which was issued to the Koppers Company. This seal, while not using oil, is another example of a rotary or circumferential gas seal.
Another gas seal is illustrated by a type GS mechanical seal manufactured by Borg Warner Corporation. A brochure depicting this seal is attached to this patent application and is also disclosed in U.S. Pat. No. 3,628,799 which was issued to Wiese. As shown, this seal is a mechanical end face seal in which sealing is effected between opposed, relative rotating, radial faces. The patent suggests the two faces are separated by a gap which permits sufficient, but controlled, leakage to effect cooling. The patentee teaches that distortion of the stationary ring must be neutralized. To accomplish this, the patentee, through conduits, directs fluid pressure to a chamber rearward of the stationary ring and its backup ring which opposes the force of such pressure upon the forward face. By balancing the pressures in the manner stated, the patentee suggests that distortions are avoided and that the leakage gap is maintained constant.
Another gas seal is depicted in U.S. Pat. No. 3,804,424 issued to James F. Gardner. The seal disclosed in this patent is also a mechanical end face seal which operates with a gap between the opposed radial sealing faces of the sealing rings to permit controlled leakage. These rings have flat, radially extending surfaces which sealingly engage one another. The surface of one of the rings is provided with a plurality of spiral grooves which extend inwardly towards a flat dam section. Under static conditions, the dam, in conjunction with the other radial face, seals the housing. Upon rotation, pressure generated by the grooves force the faces to move axially apart to define a gap which permits controlled leakage for lubrication and cooling. Gardner, like Wiese, recognized that the distortion of the sealing rings should be avoided. To this end, Gardner sought to neutralize distortion by applying pressure to one of the sealing washers.
The present invention is similar to Gardner in that it is directed to spiral groove non-contacting face seals. The general design parameters for such seals are described in the following publications:
Ralph P. Gabriel, "Fundamentals of Sprial Groove Non Contacting Face Seals", ASLE Trans, Preprint No. 78-AM-3D-1. PA1 Joseph Sedy, "Improved Performance of Film-Riding Gas Seals Through Enhancement of Hydrodynamic Effects", ASLE Trans, Preprint No. 78-LC-3B-1. PA1 1. dam width ratio between approximately 0.5 and 0.8; PA1 2. a balance of between approximately 0.8 and 0.9; and PA1 3. a groove depth of between approximately 0.0001 and 0.0003.
These articles are attached to this application for a patent and their subject matter is incorporated by reference herein.
To applicant's knowledge, end face seals have not been acceptable in gas turbines and compressors operating at high speed and pressure and having large diameters. Applicant believes such failure to arise, in part, from the inability to maintain sufficiently parallel alignment of the non-contacting faces.
Accordingly, a principle object of my invention is to provide a stable end face seal which is particularly appropriate for use in turbines and compressors having large diameter shafts and which generate high pressures. Other objectives of my invention is to provide an end face seal of the gap type which miminizes fluctuations in leakage; maintains the sealing faces in a sufficiently parallel relationship to one another, and provides a clockwise or counterclockwise couple to one washer to oppose undesired twist or deformation of that washer.